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First published online December 3, 2004
Journal of Experimental Biology 207, 4515-4524 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01289

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Kinetics and rhythm of body contractions in the sponge Tethya wilhelma (Porifera: Demospongiae)

Michael Nickel

Department of Zoology, Biological Institute, Stuttgart University, D-70550 Stuttgart, Germany

View larger version (15K): [in a new window]   Fig. 1. (A) Contraction patterns of two specimens (Tw1 and Tw2) of T. wilhelma, representing the changes in projected areas over an experimental period of 18 h. Tw1 was placed in the aquarium, Tw2 in a closed experimental reactor. Note the subcontraction (asterisk) of Tw2 at a time point when a regular contraction should have taken place if the rhythm of the former contraction series had continued; dotted lines, Tw1; broken lines, Tw2. (B) Comparison of average contraction cycle duration of Tw1 (83.3±11 min; N=12) and Tw2 (169.0±28 min; N=6).

View larger version (57K): [in a new window]   Fig. 2. Long-term recording over more than 7 days of the changes in projected area during contraction cycles of two specimens of T. wilhelma in the aquarium (A) and the open glass chamber (B). Light and dark periods are represented by white and grey backgrounds, respectively. Subcontractions, which differ significantly from regular contractions, are marked by asterisks. Experimental periods S1, S2 and S3 are represented by movies in the supplementary material. S1 represents a regular contraction series, S2 shows a series of subcontractions between regular contractions, S3 demonstrates the reaction of the sponge on a mechanical stimulation (amphipod attack). Note the adaptation phase in B after settling the sponge in the observation chamber.

View larger version (17K): [in a new window]   Fig. 3. Comparison of average contraction cycle durations during day and night for two specimens of T. wilhelma (Tw 1 and Tw 2) and for the combined datasets (Tw 1+2). Contraction cycle duration differs significantly between day and night (P=0.042).

View larger version (35K): [in a new window]   Fig. 4. Contraction kinetics of two independent datasets from two specimens of T. wilhelma (A and B), each representing the average of 12 contraction cycles. For calculations, relative contraction extent was used in order to minimize the influence on changes in the projected area by expansion and retraction of body extensions. For each contraction cycle included, time t=0 was set at the state of maximum contraction. In both cases the absolute values of maximum contraction rates are higher than the absolute values of maximum expansion rates .

View larger version (16K): [in a new window]   Fig. 5. Schematic representation of contraction kinetics and the four resulting phases of a contraction cycle in T. wilhelma. The contraction phase is shorter than the expansion phase, resulting in a higher absolute value for the maximum contraction rate than the absolute values of maximum expansion rates . The phase of maximum contraction (PC) is shorter than phase of maximum expansion (PE), see also Table 1. Variations in contraction cycle length are solely due to differences in PE.

View larger version (34K): [in a new window]   Fig. 6. (A) Local fields used to measure the spreading of local contractile waves over the sponge body. Field a represents an measurement area of 3 mm2, field b represents 2 mm2; both are not completely filled by sponge, to record changes due to contraction; distance d between a and b is 3 mm; bar, 2.5 mm. (B) Changes in the projected areas of fields a and b during a contraction event. The maximum contraction spreads as a wave over the sponge surface, taking 4 min to traverse the 3 mm distance, a speed of 750 µm min-1 (=12.5 µm s-1). The contraction used for this measurement is shown in movie S4 in supplementary material.

View larger version (59K): [in a new window]   Fig. 7. Contraction pattern and main contraction states of two fused individuals (Tw 1 and Tw 2) of T. wilhelma. (A) Both individuals in expanded phase. (B) Tw 1 in contracted phase, Tw 2 in expanded phase. (C) Both individuals in contracted phase. (C) Tw 1 in expanded phase, Tw 2 in contracted phase. Bars, 5 mm. (E) Contraction patterns of Tw 1 and Tw 2 and both together (Tw 1+2) over 24 h. A*-D* are contraction states represented by images A-D. The time-lapse series used for this measurement is shown in movie S5 in supplementary material.